Faceplates for electrostatic printing tubes are provided with pins embedded in the glass as disclosed in U.S. Pat. Nos. 2,963,606 to Crews et al; 3,157,811 to Stone, Jr. and 3,230,601 to Wurtz. These pins extend from the inside surface of the faceplate to the outside surface and the focussed electron beam scans across the inner ends and impinges upon selected ones in accordance with beam operation and the movement of a printing medium along the outside surface of the faceplate. In this manner, information can be electrostatically written on the printing medium and subsequently toned and fixed thereon.
It is important that the sections of the pins on which the electron beam impinges have sufficient areas so that they are properly engaged by the electron beam. This is necessary due to the electron beam having a very accurate linear sweep so as to enable the beam to effectively engage the electron-beam engaging areas of the pins.
Crews et al. disclose a faceplate with inner ends of the pins having more area by slanting the pins in the faceplate. The drawback with this structure is the pins are secured in position between two different types of glass and this raises the capacitance which decreases the operating speed.
The faceplate in Stone, Jr. has etched conical recesses in the inner surface of the glass in communication with the respective pins, and these conical recesses and the inner surface of the glass are coated with a conductive coating with the coating on the recesses being thinner than on the inner surface. This structure is quite complicated and the pins are all electrically connected together.
The pins in Wurtz are located in a dielectric material which is used to fuse adjacent dielectric sheets together to form a faceplate. Inner ends of the pins extend outwardly from the faceplate and they are bent in engagement with the inner surface of the faceplate so as to provide a large area for beam engagement. The capacitance is increased due to the pins being disposed in a dielectric material having a dielectric constant that is higher than the adjacent dielectric sheets.